Investigating structural-spectral interactions in managed, even-aged Eucalyptus plantations using lidar and multispectral high resolution data

The main goal of this research was to investigate the structural-spectral interactions that exist in managed, homogeneous, even-aged Eucalyptus plantations through plot-level volume and basal area modelling in Kwazulu-Natal, South Africa. Eucalyptus plantations used in this study range between four and ten years old. Small-footprint light detection and ranging (lidar; ALTM 3033 two-return laser system; 0.2 mrad footprint, 33 kHz pulse rate) and IKONOS multispectral data were collected during the spring season of 2006. Structural characterisation of 15 m radius inventory plots were performed by derivation of independent model variables from plot-level distributions of a canopy height model, lidar point heights, multispectral data, and all data sets combined. The multispectral data and lidar data were used to characterise the structural differences across a gradient of plot volume and basal area values towards determination of structural variability contribution to spectral responses. These aspects relate to the implementation of accepted remote sensing data sources for forest structure assessment and how forest structure affects model outcomes. Results for plot-level volume and basal area were encouraging using structural (lidar) data, with adjusted R² values of 0.94 and 0.82 for volume and basal area, respectively. Values for multispectral data were distinctly lower at 0.60 and 0.55 for the same dependent variables. Adjusted R² values for all data sets combined were only marginally better than lidar data with values of 0.95 and 0.88 for volume and basal area, respectively. Results show that lidar data are more amenable than a multispectral approach to forest structure assessment, although integration of the two data sources should be further investigated for scaling to larger areas.